Blank Portrait Icons and Frozen Sims in University 3- Corrupted Game?

I saw a couple of other posts with a similar problem where the portrait icons on the left just become green and the sim is frozen in place (won't do actions, can't be clicked on, etc.). But most solutions define this as just a corruption in the game and the only solution is try moving them to a new town or house, or changing them from the inactive household to the active household.

But I've tried changing them from active to inactive to active again as well as moving them out of houses and into new ones (I didn't try switching towns because I didn't realize there's a way to move a certain family between towns/games...), and it doesn't help. I've tried restarting the game and my computer and it still won't work. 

This problem happened randomly when I turned on my game today - it was working fine before. So as a test, I started a brand new town and put a copy of that family in the house. Then I quit and re-loaded that new game, and sure enough now the portraits were blank and my sims were stuck again. This seems to be a problem for just when I quit and then return to my sims, and moving them around isn't helping. 

Is there any other solution or an official mod/patch that can be downloaded?

And is there any way to prevent this? It just happened today for no reason but has always loaded perfectly fine before. I haven't downloaded any custom content except for official bonus content like the partius maximus statue.